Especially with an infant seat that is not usually kept in an extremely hot or extremely cold car for an extended period of time like a convertible would be. From a safety/liability/engineering standpoint there is no way the seat is designed to self destruct or magically be less structurally sound on May 1, 2014 than it was on April 30, 2014. I still think that a majority of the purpose of expiration dates is to favor the manufacturer rather than the integrity of the car seat. There needs to be a point when the manufacturer can stop supporting the car seat with customer service and replacement parts. I agree that there absolutely needs to be some sort of rule about when to pull car seats out of service but an absolute fixed date is a bit severe. Especially for a seat that has been well cared for by someone who knows how to take care of a car seat (not checking on an airline, not washing straps, and the like).
Agreed that it won't self destruct on said date. And agreed that Graco's dating method was dumb. LOL
But the base *is* left in the car. One of the main, and BEST arguments against continuing to use a seat past it's expiration is that it has been exposed to the heat and cold, which the base definitely has. Over time, the plastic does degrade. No one can guarantee to you at what point that plastic will have degraded enough to fail in a crash. The manufacturer is saying that they back the seat for 6 yrs against failing in a crash. Any longer than that, and they do not back it and they do not know the consequences. If it does fail in a crash, even if it's only the plastic of the base that does, the infant seat could rebound more forcefully...it could come off the base and fly through the air....it could twist sideways...the whole seat could hit someone else in the car and kill them. If the plastic of the seat itself fails, the harness could be ripped loose and the child thrown out. We don't know exactly what will or will not happen. But it may not work properly. It isn't worth that chance. It seems that many newer seats have longer expiration times and appear to be made w/a sturdier plastic. Over many years, manufacturers know more about these things.
But there area many good reasons not to use seats beyond their expiration dates.